Pick-off for electrical control systems



Patented Oct. 24, 1950 SYSTEMS PICK-OFF FOR ELECTRICAL CONTROL Spencer Kellogg, 2nd, and Gerald N. Hanson,

Glen Head, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Original application February 13, 1942, Serial No.

430,736. Divided and this application 10, 1945, Serial No. 582,134

4 Claims. 1

The present invention is concerned with pickoff or control signal generators which are adapted for controlling servomotors of positioned or follow-up control systems, including systems for the simultaneous control of aircraft altitude. automatic level flight and constant rate of climb or glide control, described and claimed in a copending application now U. S. Patent No. 2,415,429, dated February 11, 1947, for Aircraft Altitude Control, of which this application is a division.

It is an object of the present invention to improve such signal generators or pick-offs, which are usually of the alternating current type and control reversible servo or follow-up motors, so that such pick-offs remain operative to control the motor throughout a 360 degree difference in rotation of the controlling and controlled elements. More particularly, our invention is an improvement of the E type of alternating current transformer pick-off, such as shown, for instance, in the prior patent to Wittkuhns, No. 1,921,983, dated August 8, 1943, for Follow-up Device for Gyro Compasses in which control is lost if the controlling and controlled elements are separated more than a few degrees in their angular relationship.

A still further object of the present invention is to provide improved electrical pick-offs including means for zeroizing when not in use.

Further objects and advantages of the present invention will be apparent from the attached specification and drawings in which,

The single figure shows one embodiment of the system of the invention.

Referring to the drawings, there is shown the system of the invention as applied to an electrically controlled servo system for automatically controlling aircraft, such as shown in U. S. Patent No. 2,398,421 for Electro-Hydraulic Servo System,

issued on April 16, 1946, in the name of C. A. Frische, G. P. Bentley, and P. Halpert. This patent shows an automatic pilot system in which a reversible-phase, variable magnitude, alternating signal voltage is produced corresponding to a desired control action. This signal voltage is then amplified andactuates, a suitable electrical or hydraulic servo system, whereby the craft controls are operated in direction and extent in accordance with the phase and magnitude of the I signal voltage. Although the prior applications were disclosed primarily with respect to rudder control, it will be clear that the same control systems may be used for elevator or aileron control of aircraft, or for the control of a servo or March follow-up motor for any purpose. In the present invention such a system is used for the elevator control, whereby the altitude of the craft may be suitably controlled.

In the drawings, reference numeral IOI shows a sealed bellows type of barometric unit which, as is well known, will expand or contract in accordance with the pressure to which it is subjected. Barometric unit MI is preferably not completely exhausted but left with a very small remaining air pressure of the order of a few millimetres of water, being just sufficient to compensate for the effect temperature changes in expanding and contracting the bellows WI and the housing and mounting of the unit to be described. and thereby rendering the unit independent of temperature, as will be described.

This unit is entirely enclosed in an air tight housing indicated generally by dotted line I02, which is connected as by a duct I04 to a source of Pitot static pressure whereby the bellows IN is subiected to only the static air pressure outside the craft and accurately indicates by its expansion the altitude of the craft. One end I03 of the bellows is fixed to the craft as at I06 by means of a fiat spring I08. The other end I05 of bellows IOI is attached to a link I01 which is thereby translated in accordance with the altitude of the craft. Link I01 is pivotally connected as at I09 to a crank arm I I I which is rigidly fastened to a shaft 3 journalled in a bearing II5 fixed to the craft. Spring I08 permits the necessary deviation of shaft I 01 as the bellows expands and contracts, but is stiff enough to transmit the expansion of bellows IN to shaft I01. Fastened to the shaft H3 is a gear sector II1 meshing with a pinion II9 fixed to a shaft I2I.

Shaft I2I actuates the sensitive element of a pick-off device I24, shown as an armature member I23 formed as a semi-cylinder of magnetic material. Coaxial with shaft I2I and pick-off armature member I23 is the pick-off housing I25 containing four field poles symmetrically located, each having wound thereon a coil such as coils I21, I29, I3I and I33, respectively. These poles are equally spaced about the axis of the pick-off device, one pair of opposite coils I3I and I33 being connected in opposing series relation to output wires I35 while the remaining pair of coils I21 and I29 are energized from a suitable source I31 of alternating current in such manner as to simultaneously provide like magnetic poles.

It will be clear that with pick-off armature I23 in the central and symmetrical position shown in the drawings, equal voltages will be induced aeeaeee in pick-up coils I3I and I33, resulting in new voltage across output wires I35. If pick-o8 armeture I23 is displaced from the position shown in, either direction the voltage induced in one of cells I 3I, I33 will be greater than in the other and the resulting unbalance will appear as a variable magnitude reversible phase alternating voltage across output wires I35.

Pick-oil I25 therefore acts to convert the relative displacement between armature I23 and housing I25 into an alternating signal voltage corresponding in phase to the sense of this displacement and in magnitude to the magnitude of the displacement. The relation between signal magnitude and displacement magnitude may be made to have any desired form, as by suitably forming the pole faces of housing I25. If these pole faces are formed cylindrically and concentric with the axis of armature I23, the signal will vary linearly with angular displacement until the armature I23 clears the poles. Thereafter, the signal will remain substantially constant with increased displacement. If the pole faces are formed flat, as shown, the signal will increase more rapidly for small displacements, and will asymptotically approach the substantially constant value for large displacements. Other forms may be used, suited to the particular use of the pick-ofi, which is in no way restricted to the use here shown.

It will also be clear that the voltage appearing across output terminals I35 will maintain the same phase during displacements of pick-oi! armature I 23 in either direction from the central position up to 180 degrees in magnitude, so'that for a full 360 degrees of rotation of armature I23, a useful voltage output will be obtained from this device. However, where it is not necessary to provide more than 90 degrees of useful control signal, one of the two energizing poles may be eliminated.

The output signal voltage appearing between output wires I35 is used as a control voltage for the aircraft elevators 85 in the same manner as shown in the above-mentioned Patent No. 2398321. As is therein shown, the reversible phase variable magnitude signal voltage, such as the voltage appearing between wires I35 is fed to a suitable phase sensitive amplifier and rectifier I59 whose output controls an electrical torque motor and/or an electrical or hydraulic servomotor unit IGI to actuate the elevators 55 of the craft to effect a change in altitude. It will be understood that with the switch I51 in the up position the signal voltage appearing between wires I35 may be combined without or within the amplifier I59 with the signal voltage from the automatic pilot so that the altitude control signal will be in continuous operation through the automatic pilot controls. This action will continue until the altitude has changed by such an amount that the expansion or contraction of bellows IIlI, operating through magnifying linkage I01, III and gearing II1, II! has restored pick-off armature I23 to a central or balanced position with respect to pick-off housing I25 and its coils, at which time the signal across terminals I35 disappears and the elevators 85 return in their centralized position. Thereafter, the craft will maintain constant altitude, as any change in altitude will at once operate to drive the craft back to its original altitude.

Since shaft I2I is actuated directly from bellows IOI, it will be clear that its position is indicative of the craft altitude. Hence, a suitable altitude indicator could be actuated directly from this shaft. Also, since pick-oi! housing I25 is caused to follow-up pick-oi! armature I23 which is connected to shaft I2I, its position also is indicative of altitude, and a suitable indicator may be provided therefor.

In order to permit adjustment of the automatic constant altitude control just described. housing I25 has formed on or fixed to the outside thereof a gear I35 and may be positioned from an altitude control I43, as by way of shaft I55, gear I51, diflerential I55, shaft I5I and differential I".

In operation, the operator will set the housing I25 in the position corresponding to the desired altitude as by means of altitude control knob I. If the craft is not already at this altitude, pick-off armature member I23 will not be centralized with respect to housing I25 and accordingly a voltage will be produced across terminals I35 corresponding to the desired sense of change of altitude and corresponding in magnitude, at least up to the maximum output of the pick-oi! device, to the desired amount of change of altitude. This signal voltage appearing across terminals I35 will operate as described above to reposition the craft in altitude until bellows IIII recentralizes armature I23. The maximum signal output of pick-off I25 may be chosen so that the resultant actuation of the craft elevators will not produce too steep a change in altitude.

If a constant rate of climb or glide is desired, this may be provided by continuously rotating pick-oil housing I25 at a constantrate. when this is done, the craft, as described above, is controlled to change its altitude to maintain pick-off armature I23 centralized with respect to housing I25 and hence the craft must continuously rotate shaft I2I by changing its altitude at the same rate as housing I25. Such a constant rotation of housing I25 is obtained from a constant speed motor I53, which drives a disc I65 forming a part of a ball and disc type of variable speed drive I51. Cylinder I11 is connected to a shaft I1! and by way of a gear I3I to the third member diilerential I55, and thence to housing I25. By this means pick-oi! housing I25 is continuously rotated at constant speed from constant speed motor I53, the speed of rotation depending upon the setting of ball carriage I1 I by means of an altitude rate control I59. It will be clear that any other suitable type of variable speed drive may be used here, such as that shown in copending application Serial No. 428,030 new patent No. 2,526,665, dated October 24, 1950, filed January 24, 1942, in the names of H. L. Hull. R. C. Goertz, and W. C. Hartman for Positioned Control System. There is thus provided a climb and glide control having adjustable constant rates of climb or glide, which may be indicated on the altitude rate dial I12 cooperating with a fixed index I15 and rotated by altitude rate control I 69.

Itwill be seen that the motion of arm I01 connected to bellows IOI will not vary linearly with altitude because of the non-linear variation of atmospheric pressure with altitude. In order that the same sensitivity of control may be obtained at different altitudes and in order that the rate of climb or glide produced in the manner just described be constant over wide ranges of altitude, non-linear linkage II", III is provided, being in effect an eccentric connection, and providing the proper non-linear motion of shaft I51 with respect to altitude to result in a linear traction of the casing I02 housing the system,

so that the separation, for instance, of bracket I I5 and fixed support I06 of bellows IUI will vary, as will the bellows IIJI due to change in size of its metal container. Such action would produce an apparent rotation of shaft I I3 with respectto bracket H5, and would therefore efiect a change of position of pick-oil armature I23, and the craft would change its altitude in the manner described. To prevent this action, a slight amount of air is left within bellows Illl so that temperature changes will cause an increase or decrease of pressure within the bellows IOI, resulting in the slight extension of retraction just necessary to compensate for the effect of the expansion or contraction of casing I02 and bellows IOI just described. The system is thereby effectively compensated against temperature effects.

In order to prevent too great and too sudden a change in altitude upon first activating the automatic altitude control, it is desirable to maintain pick-oil armature I23 continuously centralized with respect to pick-oil housing I25 when the altitude control is not in use, so that activation of the altitude control will merely result in automatic level flying at the attained altitude. One manner of producing this result is included in the drawings. Thus, the output signal voltage appearing between wires I 35 is connected to a double-pole double-throw switch I51. In its upper position, this switch connects the signal voltage to amplifier I59 to control the elevators 85 in the manner already described. In the lower position of switch I51, the signal voltage is now connected instead through an amplifier I62 of any suitable type and doublepole double-throw switch I64 (when in the up position) to a motor I66 connected to rotate housing I25, through the third member of differential I40. Motor I56 is illustrated as being of the two phase induction type, having one field winding energized directly from a source I68 of alternatingcurrent and its second field winding fed from the output of amplifier I62 when switch IE4 is in the up position. Suitable means are provided either in amplifier I62 or motor I56 to insure that the energizations of the two windings will be in phase quadrature. It will be clear that any suitable type of reversible motor I66 may be used; if a D. C. motor is used, the output of amplifier I62 should then provide reversible polarity D. C. output.

The system described provides in effect a closed follow-up system whereby the motor I66 continuously drives pick-off housing I 25 to follow the position of piek-ofi armature I23 as altitude changes. In this way, when the craft, for instance, first takes off, with the automatic altitude control unenergized,. the pick-off I23 is kept continuously centralized or zeroed so that, after attaining any desired altitude, the operator may immediately actuate the altitude control merely by throwing switch I51 from the down to the up position, and thereby have the automatic altitude control at once take over and maintain the attained altitude of the craft without any sudden changes.

When switch IE4 is in the down position, motor I66 is energized directly from power source I68, and will rotate continuously, thereby rotating pick-off housing I25. This provides an altitude control equivalent to control I43, but now power-operated. Switch I64 may be positioned at any suitable control point, remote from the entire apparatus, if desired. It may be made as a switch biased or normally in the up position and momentarily operable to the down position b the operator to cause a change of altitude when the automatic pilot is in operation.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electrical pick-off device comprising a housing four field poles symmetrically and radially disposed within said housing, a winding upon each of said poles, at semi-cylindrical magnetic armature member having its axis symmetrically disposed with respect to said poles, means for energizing one opposed pair of said windings by alternating current in such manner that the pair of poles corresponding to said pair of windings simultaneously exhibit like magnetic polarity, and means for connecting said other pair of windings in series opposition whereby there is produced across said series connected windings a reversible-phase variable magnitude alternating signal voltage corresponding in phase and magnitude to the sense and magnitude of the relative displacement between said armature and said housing.

2. An electrical pick-off device as in claim 1 further comprising means for rotating said housing independently of said armature.

3. An electrical pick-off device comprising a housing, four field poles symmetrically and radially disposed within said housing, coil windings on the poles, a semi-cylindrical magnetic armature member coaxial with said poles, means for opposite A. C. energization of one opposed pair of said field pole windings, and output means oppositely connected to the windings of the other opposed pair of poles whereby there is produced in said output a reversible-phase variable magnitude alternating signal voltage corresponding in phase and magnitude to the sense and magnitude of the relative displacement between said armature and said housing, through a complete rotation of the armature and housing.

4. In a follow-up system having a sensitive pick-off from the reversible phase variable magnitude alternating slgnalvoltage supplied thereto from the differential output of the second pair of field windings.

SPENCER KELLOGG, 2ND. GERALD N. HANSON.

L (References on following page) REFERENCES CITED Number The following references are of record in the file of this patent:

UNITED STATES PATENTS 5 Number Name Date gg a 1,921,983 Wittkuhns Aug. 8, 1933 8 Name Date Urter Sept. 8, 1936 Helpert et a1. Feb. 18, 1947 FOREIGN PATENTS Country Date Germany July 19, 1932 

